Conventionally, various accumulator fuel injection devices (CRSs: Common Rail Systems) using pressure accumulators (common rails) have been proposed in order to inject high-pressure fuels efficiently in diesel engines and so on.
For instance, as shown in FIG. 25, for switching the pressures of a pressure accumulator depending on the driving conditions of an engine, JP 06-93936 A has proposed an accumulator fuel injection device having a first pressure accumulator 236 responsible for a main injection and a second pressure accumulator 278 responsible for a pilot injection. These pressure accumulators 236, 278 are switched by a switching device 286 to carry out a fuel injection.
For obtaining the injection pressure perfect for engine performance, JP 2885076 B has proposed an accumulator fuel injection device having a pressure-amplifying piston for amplifying the pressure of a fuel and a cylinder chamber, located between a pressure accumulator and a fuel injection valve.
More specifically, as shown in FIG. 26, there is disclosed an accumulator fuel injection device 380 that comprises: a pressure accumulator 395; an oil supply channel 360 for a fuel; an oil control channel 361; a switching valve 362 for fuel injection control; a pressure amplifying piston 378 for elevating the fuel pressure to 70 to 120 MPa (approximately 700 to 1,200 kgf/cm2); a cylinder chamber 383 for housing the pressure amplifying piston 378; a hydraulic circuit 363; a piston-work switching valve (three-way solid valve for amplifier) 364; and a controller (not shown).
However, the accumulator fuel injection device disclosed in JP 06-93936 A needs to be provided with two kinds of the pressure accumulator, their switching device, and so on. Therefore, there is a problem in that the accumulator fuel injection device is complicated and grown in size. In the accumulator fuel injection device, furthermore, there is another problem in that the lubricant prevents the movement of a plunger and fuel having a large flow rate cannot be pressurized sufficiently because of lubricant cannot travel forward and backward freely between a spring-holding member and a cam chamber when the cam and plunger of the fuel supply pump are driven at high speed. As the flow rate of fuel is restricted, a large amount of fuel cannot be pressurized sufficiently.
For the accumulator fuel injection device disclosed in JP 2885076B, a pressure amplifying piston is placed between the pressure accumulator and the fuel injection valve to intend to provide a multi-stage pressure injection. In this case, there is also proposed a pressure pump for supplying high-pressure fuel to the pressure accumulator. However, such a pressure pump is one of the conventional pressure pumps used for the conventional accumulator fuel injection devices. Any pressure pump, which intends to supply a large amount of high-pressure fuel, is not designed.
Therefore, as a result of concentrated study, the present inventors has found out that, by providing a penetration portion between a spring-holding chamber and a cam chamber, a large amount of a fuel oil can be sufficiently pressurized even when the cam and the plunger are driven at high speed because of allowing a lubricant or a fuel for lubrication to move forward and backward without restraint.
Specifically, an object of the present invention is to provide a fuel supply pump enough to pressurize fuel by driving a cam and a plunger at high speed without allowing a lubricant or a fuel for lubrication to inhibit the movement of a plunger even in the case of enlarging the amount of fuel discharged, and to provide a tappet structural body suitable for such a pump.